To date, there have been few comparative studies evaluating the safety of different vaccine schedules. A few of the existing studies show that there are cases in which the risk of adverse events depends on the vaccination schedule used. Hence, it is both a feasible and important area of study. As a relatively new field of investigatio, the big question is what types of study designs will be most appropriate for evaluating different childhood vaccine schedules. In this project, we will develop, evaluate, compare and illustrate a wide variety of new epidemiological methods for studying the safety of childhood vaccination schedules, with respect to a wide variety of different aspects and components of the vaccine schedule. These include the timing of individual vaccines; the timing between doses of the same vaccine; the interaction effect between vaccines and concurrent health conditions or pharmaceutical medications; the interaction effects of different vaccines given on the same day; the ordering of different vaccines; and the effect of cumulative summary metrics such as the total number of vaccines or the total amount of some vaccine ingredient. The project also covers study designs for the comparative evaluation of the CDC recommended schedule, popular alternative schedules and completely unvaccinated children. Methods will be developed for both adverse events with an early onset, which are the easiest to study, and for adverse events with a late onset, including serious chronic conditions.